1. Field of the Invention
The present invention relates to a measurement gauge for an orifice meter which is used in the measurement of fluid flow. In particular, the present invention is directed to a measurement gauge to determine whether an orifice meter is in compliance with certain minimum and maximum tolerances wherein the measurement may be taken without disassembly of the meter tube.
2. Background of the Invention
It is well known that a fluid, such as natural gas, flowing through a pipe, or other closed conduit, can be measured by placing a restriction, such as an orifice plate, inside the pipe or closed conduit to cause a reduction in pressure (pressure drop) as the fluid flows through the opening in the orifice plate. This pressure drop is known as the differential pressure. There is a relationship between the amount of this pressure drop and the rate of fluid flow through an opening in the orifice plate and, therefore, the meter tube as well as the pipe or closed conduit.
Bernoulli first theorized that energy cannot be destroyed but only changed from one form to another. In the orifice meter, potential energy is converted into kinetic energy. Hence, the equation: ##EQU1## where the velocity of fluid (V) passing through the orifice is equal to the square root of 2 times the product of gravity (G) multiplied by the head (H).
In a typical orifice meter, an orifice plate having a restricted circular orifice is inserted perpendicular to the flow through the meter tube. A first pressure tap hole is placed immediately upstream of the upstream face of the orifice plate. A second pressure tap hole is placed immediately downstream of the downstream face of the orifice plate. The pressure taps are connected to a recording device (or electronic differential pressure transmitter or transducer) by use of tubing or small diameter pipe so that the differential pressure may be measured, sensed or recorded. This differential pressure is utilized to determine the rate of flow through the opening in the orifice plate and, therefore, the meter tube as well as the pipe or closed conduit.
Allowable variations in the location of the pressure taps are specified by API and ANSI Standards (see ANSI/API Standard 2530, published 1985, also called AGA Report Number 3, and API Manual of Petroleum Measurement Standards, Chapter 14.3, Part 2, February 1991). The location of the taps is critical not only to meet the standards but to accurately measure the flow of fluid. Accurate measurement of the flow is important for a number of reasons. Initially, API, AGA and ANSI standards set minimum and maximum tolerances allowed so that orifice meters attempting to meet these standards must be in compliance. Additionally, since pipeline companies increasingly transport gas for other entities, the payments will be directly dependent upon the flow of gas so accurate measurement is important. Finally, taxes and royalties are computed from the flow of gas. In summary, the measurement of fluid flow through a pipeline applies to the production, processing, transportation and distribution of fluids.
Accordingly, it is a principal object and purpose of the present invention to provide a measurement gauge device for an orifice meter.
It is a further object and purpose of the present invention to provide a measurement gauge device which may be used within a pipeline without completely disassembling the orifice meter or the pipeline.